From: Qianchang Zhao <pioooooooooip@gmail.com>
Date: Sun, 9 Nov 2025 01:00:55 +0000 (+0900)
Subject: ksmbd: skip lock-range check on equal size to avoid size==0 underflow
X-Git-Tag: v6.19-rc1~163^2~27
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5d510ac31626ed157d2182149559430350cf2104;p=thirdparty%2Flinux.git

ksmbd: skip lock-range check on equal size to avoid size==0 underflow

When size equals the current i_size (including 0), the code used to call
check_lock_range(filp, i_size, size - 1, WRITE), which computes `size - 1`
and can underflow for size==0. Skip the equal case.

Cc: stable@vger.kernel.org
Reported-by: Qianchang Zhao <pioooooooooip@gmail.com>
Reported-by: Zhitong Liu <liuzhitong1993@gmail.com>
Signed-off-by: Qianchang Zhao <pioooooooooip@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
---

diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
index 891ed2dc2b735..90e693e4e4149 100644
--- a/fs/smb/server/vfs.c
+++ b/fs/smb/server/vfs.c
@@ -324,6 +324,9 @@ static int check_lock_range(struct file *filp, loff_t start, loff_t end,
 	struct file_lock_context *ctx = locks_inode_context(file_inode(filp));
 	int error = 0;
 
+	if (start == end)
+		return 0;
+
 	if (!ctx || list_empty_careful(&ctx->flc_posix))
 		return 0;
 
@@ -828,7 +831,7 @@ int ksmbd_vfs_truncate(struct ksmbd_work *work,
 		if (size < inode->i_size) {
 			err = check_lock_range(filp, size,
 					       inode->i_size - 1, WRITE);
-		} else {
+		} else if (size > inode->i_size) {
 			err = check_lock_range(filp, inode->i_size,
 					       size - 1, WRITE);
 		}